In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength (and increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in the mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a shorter wavelength (and a higher energy level) than these excimer lasers, such as F2 excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X-ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material that satisfies these conditions, a chemically amplified resist composition is used, which includes a base component which exhibits changed solubility in a developing solution under the action of acid and an acid generator which generates acid upon exposure.
For example, in the case where the aforementioned developing solution is an alkali developing solution (namely, an alkali developing process), a chemically amplified positive resist containing, as a base component (base resin), a resin which exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator is typically used. If the resist film formed using the resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, acid is generated from the acid generator component, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution. The unexposed portions remain as a pattern, resulting in formation of a positive-type pattern. The aforementioned base resin uses a resin for which the polarity increases under the action of acid, resulting in an increase in the solubility of the resin in an alkali developing solution, but a decrease in the solubility of the resin within organic solvents. Accordingly, if a process that uses a developing solution containing an organic solvent (an organic developing solution) is employed (hereinafter also referred to as a solvent developing process or negative-type developing process) instead of the alkali developing process, then within the exposed portions, the solubility in the organic developing solution decreases relatively, meaning that in the solvent developing process, the unexposed portions of the resist film are dissolved in the organic developing solution and removed, whereas the exposed portions remain as a pattern, resulting in formation of a negative-type resist pattern. Patent Document 1 proposes a negative-type developing process.
Currently, resins and the like that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now widely used as base resins for resist compositions that use ArF excimer laser lithography or the like, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 2).
Further, all manner of acid generators have been proposed for use in chemically amplified resist compositions, and known acid generators include onium salt acid generators, oxime sulfonate acid generators, diazomethane acid generators, nitrobenzylsulfonate acid generators, iminosulfonate acid generators, and disulfone acid generators. Among these, as the onium salt acid generators, iodonium salts having an iodonium ion as the cation and sulfonium salts having a sulfonium ion as the cation are conventionally used. In recent years, acid generators having a sulfonium salt with a lactone structure have been proposed (for example, see Patent Documents 3 and 4).